The aim of this study was to investigate the pathological substrate of temporo-polar blurring. The study involved 32 consecutive patients with medically intractable TLE and HS who underwent surgery. They were divided into two groups on the basis of the presence/absence of temporopolar blurring. Surgical specimens were examined neuropathologically and selected samples from both groups underwent high-field 7T MRI and ultrastructural studies. At clinical level an earlier age at epilepsy onset and a longer duration of epilepsy was found in the patients with blurring. Blurring was also associated with lower neuropsychological test scores, with a significant relationship to abstract reasoning.

7T MRI examination showed only in those patients with blurring a dishomogeneous signal in the white matter, with patchy areas of hyperintensity. Sections from the patients with blurring that were processed for myelin staining revealed dishomogeneous staining of the white matter, which was confirmed by analyses of the corresponding semi-thin sections.

Ultrastructural examinations revealed the presence of axonal degeneration and a significant reduction in the number of axons in the patients with blurring.

These data provide robust evidence that temporo-polar blurring is caused by the degeneration of fibre bundles, and suggest slowly evolving chronic degeneration with the redistribution of the remaining fibres.